Materials Science Forum Vol. 978

Abstract: Glass fibre reinforced epoxy (GRE) composites, used as mechanical support and thermal insulators for superconducting magnets of fusion reactors, have been exposed to gamma irradiations at both higher and lower order ranges of doses. Hand layed E-glass fibre/epoxy composite samples, exposed to gamma-irradiations of cumulative doses of both low strength (10, 20, 30, 40, 50 and 60 kGy) and high strength (0.5, 2.5, 6.5, 8.5 and 10.5 MGy) reveal a huge lowering of the ILSS (inter laminar shear strength) for its exposure to low strength dose irradiation. However, improved ILSS values are recorded for high dose exposures. At both high and low doses of exposure to irradiation the T_g (glass transition temperature) got improved initially with a decreasing trend towards the later stages of exposures. Thermo-gravimetric analysis (TGA) test reveals lowest initial decomposition temperature (IDT) for the composite sample irradiated to maximum dose (10.5 MGy). Activation energy () values of gamma-irradiated composite samples for thermal decomposition were found less compared to that for as-cured composite. FTIR spectra of irradiated samples reveal formation of oligomers confirming the trend of activation energy of irradiated composite. FESEM fractographs of the irradiated composite fracture samples reveal several modes of failure.

Abstract: Carbon fibre reinforced polymer (CFRP) composites a perfect structural material due to their outstanding malleable strength, great rigidity, light mass and pronounced thermal resistance. But their inferior out-of-plane properties which are controlled by the matrix–fibre interface restrict the use of CFRP composites in critical applications. Amalgamation of nanofiller in the CFRP composites has found to improve the matrix-fibre interface and there by out-of-plane response. Though matrix modification has contributed to the improvement of interface, fibre modification has a scope for higher levels of nanofiller incorporation and proper fibre nanofiller adhesion. Out of several methods available for fibre modification electrophoretic deposition (EPD) is an eye-catching method for monitoring as well for nanofiller deposition. In recent ages, Graphene has grabbed wonderful consideration Among the graphene based functionalised nanofillers Carboxyl functionalized Graphene (G-COOH) modified CFRP composites have shown better ILSS properties. This research primarily aims to fabricate a CFRP composite using G-COOH modified carbon fibres with varying nanofiller concentrations of 0.5g/ltr, 1g/ltr and 1.5g/ltr in the EPD bath and its impact on the mechanical properties of the FRP composites. The laminates thus obtained were subjected to short beam shear test for the determination of inter laminar shear strength (ILSS). Fractography of the tested samples to observe various failure modes has been carried out by using scanning electron microscope (SEM).

Abstract: The objective of this research is to evaluate the temperature dependent strengthening mechanism of 0.5 wt.% carbon nanofiber reinforced glass fiber/epoxy (CNF-GE) as a function of environmental temperature. Flexural response of the CNF-GE composite has been studied at 30°C, 70°C and 110°C temperatures and compared over control glass fiber/epoxy (GE) composite. When flexural test was conducted at room temperature, CNF-GE composite exhibited about 29% improvement in strength, over control GE composite. With increase in environmental temperature, the extent of strength enhancement continued to decrease and at 110°C, the strength of the CNF-GE composite was found to be about 12% lower than control GE composite. Visco-elastic properties of CNF-GE and control GE composites have also been studied in the temperature range of 40 to 200°C.

Abstract: Moisture absorption of natural fiber-based composites is one of the major problems in outdoor applications. The present study deals with the effect of moisture absorption on mechanical and thermal properties of unmodified/modified Date Palm Leaf (DPL) with glass fiber-based hybrid composites. Natural fibers were modified with alkaline treatment to improve fiber and matrix bonding. Conventional hand lay-up technique is used to fabricate the composites with varying different wt.% of treated and untreated short DPL with constant wt.% of glass fiber and prepared with random oriented manner. The combine effect of hydrophilic and hydrophobic nature find out as the study based upon the natural with synthetic fiber hybrid composites. Mechanical behaviour of the epoxy-based hybrid composites were characterized by using tensile, flexural and hardness test. The results revealed that significant improvement in mechanical properties by the addition of different weight percentage of modified DPL. Different thermal properties of the composites were described by using Thermo Gravimetric Analyzer (TGA) and Differential Scanning Calorimetric (DSC). Morphological investigation was carried out to by using scanning electron microscope. All the properties of untreated natural fiber reinforced composites were mostly affected by the influence of water absorption as compared with chemically treated based composites.

Abstract: The present study is mainly aimed at investigating the distribution of in-plane stresses of a rectangular plate under localized uniform in-plane tensile loading through finite element analysis. The configuration used in the analysis is analogous to the case of premature failure of stiffened panel due to the termination of a stiffener in aircraft wing structure. In this current work, three different types of materials namely, isotropic, plain woven and transversely isotropic materials are being considered. Aluminium is taken as isotropic; high strength carbon/epoxy is being assigned as plain woven composite and carbon nanotube based hybrid composite is used as transversely isotropic material, due to their wide range of applications in aircraft structures. The effect of different materials on overall axial, transverse and shear stress distributions at different layers of the stiffened composite panels are demonstrated using finite element analyses. Further, the variations of these stresses along axial and transverse directions are also compared for different materials. It can be concluded from the present study that the peak stress developed near the load application zone should be incorporated in the design criteria of such plates to avoid failure.

Abstract: Molecular dynamics (MD) simulations of metal-metallic glass (Al-Cu₅₀Zr₅₀) multilayer during nanoindentation is carried out to investigate the load-displacement response, mechanical properties and deformation mechanisms. The indentation study is carried out at temperatures in the range of cryogenic to room temperature (10 K-300 K). The indenter speeds are varied between 0.5-5 Å/ps to study the effect of loading rate. The interaction between Al-Cu-Zr atoms are defined by EAM (Embedded Atom Method) potential. A sample size of 200 Å × 200 Å × 200 Å (in x y z-direction) comprising of 538538 atoms is used for nanoindentation. P P S boundary condition (BC) in x y z direction and NVT ensemble are used. We observed a peak load of 117 nN, at a temperature of 10 K with a loading rate of 5 Å/ps. We found that as the loading rate increase, the peak load also increases. As anticipated, the increase in temperature decreases the strength of the multilayer. The atomic displacement vector plots reveal that MG act as hurdles to the movement of dislocations nucleated at the interface.

Abstract: Polyvinylidene fluoride (PVDF) – Lead Zirconate Titanate (PZT) is a polymer composite that is becoming increasingly popular in micro-scale sensors and actuators because of its unique properties such as high flexibility, low density and high piezoelectric constants. However, lead-based piezoceramics, despite their superior properties, are toxic and are known to damage the environment, and as such a conscientious effort is being made by the scientific community towards replacing lead-containing piezoceramics with environmentally-friendlier and lead-free piezoceramics. Barium Titanate (BaTiO₃) is one such piezoceramics that is widely studied today to be a potential replacement of PZT in many applications. As such, in this work, effort has been made to predict the effective mechanical, dielectric and piezoelectric properties of PVDF-BaTiO₃ composite system using Finite Element Method (FEM). Kinematic Uniform Boundary Conditions (Displacement and Voltage) are used for this analysis. For evaluation of the effective material constants of the composite, several types of representative volume elements are considered. The effects of volume fraction, effect of the size of the micro-particles i.e. mono-modal versus multi-modal size distribution, effect of periodic versus quasi-random distribution of microparticles in the matrix, the effect of clustering of the particles, effect of orientation of the microparticles i.e. unidirectional or randomly oriented are discussed. Finally, a comparison of properties between PVDF-PZT and PVDF-BaTiO₃ is made, so as to see whether PVDF-BaTiO₃ can be a potential replacement for PVDF-PZT composite.

Abstract: The present work deals with the finite element simulation of drilling of fibre-reinforced composites. The simulation is done using commercially available software. Hashin failure criteria has been used to simulate the drilling process. Three dimensional drill model was created and Hashin failure is defined via VUMAT sub-routine. Three-dimensional Hashin failure have larger stress and strain analysis resolution. This research is focused on validating reaction force and accuracy of drill. Reaction force obtained in composite drilling simulation is compared with experimental data. The work is focused on reproducing the simulation of composite modelling and composite damage rather than theoretical explanation of composite material and mathematical model behind the simulation. Thus, laying the knowledge to simulate composite fibres failure.

Abstract: Multiferroics, with two or more coexisting ferroic orders (ferroelectric, ferro (antiferro)-magnetic) in a single phase, display promising photovoltaic characteristics which can be utilised in solar energy harvesting. However, the efficacy is seriously challenged due to their wide band gap, far from the ideal value of ~1.52 eV for photovoltaic applications, resulting in overall unimpressive performance. In the present work, an approach towards imparting multiferroism in an otherwise non-ferroic system was adopted through strain engineering. Bulk SrMnO₃ (SMO) is antiferromagnetic-paraelectric. However, our previous first-principles studies predicted high-pressure phase transformation from bulk non-polar phase to a tetragonal polar phase. In light of the above, SMO was synthesised hydrothermally at 200°C for 96 h using water-soluble nitrate salts of strontium and manganese. FESEM study reveals the formation of hexagonal bipyramid shaped SMO crystals with elongated 1-D features. Powder x-ray diffraction studies and subsequent Rietveld refinement confirm the presence of hexagonal (P6₃/mmc) as well as tetragonal (P4mm) phases. Energy dispersive x-ray analysis (EDAX) confirms Sr/Mn ≈ 1, the stoichiometric ratio. UV-VIS spectroscopy was utilised to estimate the optical bandgap of the as-grown sample which was found to be in the range of 1.4-1.5 eV. Temperature-dependent magnetisation plot indicates the magnetic transition temperature, ~275K.

Abstract: The materials significantly influence the structural, optical and photoelectrical characteristic. Materials such as Arsenic selenide, Tellurite Glass, Silicon carbide, Silicon dioxide and Silicon nitride are investigated through finite element method. The models are established to analyse the structural behaviour of polarization preserving fibre of proposed materials. Photoelectric characteristic determines guided properties of photon particles. Refractive index of the materials influences the properties of photonic crystal fibre. A Polarization Splitter based hexagonal structure is proposed, where inner ring of cladding is in elliptical shape air holes and outer rings are in circular air holes. It provides highly negative dispersion, low confinement loss and high nonlinear coefficient between 1µm to 2µm wide wavelength ranges. The dispersion result shows -2000 db/km-nm at 1.55µm wavelength. Polarization beam splitters photonic crystal fiber characteristics of proposed materials are analysed with same structural parameters.